Rovers extended their unbeaten run to five games with a goal in the first half, Craig Conway, on his full debut, driving in a low angled shot that went in via the outstretched leg of Reading skipper Jobi McAnuff to seal a 1-0 success.
Reading's traditional end-of-season surge had appeared to be gathering momentum, with five victories in their previous seven matches and 19 goals scored.
Fortune had also seemed to be on their side, with centre-backs Alex Pearce and Kaspars Gorkss both having recent red cards rescinded by the Football Association.
Pearce was sent off in the 2-0 home defeat by Sheffield Wednesday and Gorkss in the 3-1 win against QPR at Loftus Road last Sunday.
Blackburn were hoping to make a late charge for the play-offs and were unbeaten in their previous four games, three of them draws. And they had not lost to Reading in their past eight meetings.
Rovers made a bright start in the sunshine at the Madejski Stadium, with winger Conway making a series of penetrative runs along the left flank.
But there was little end product and Reading created the first decent chance when Pavel Pogrebnyak fed McAnuff wide out on the left.
McAnuff cut in, making space for a shot, but his effort was weak and caused little trouble for Blackburn goalkeeper Paul Robinson. It set the tone for a lacklustre first half that only burst into life near the interval.
Rovers had threatened only sporadically, Rudy Gestede firing wide from a good opening, when they went ahead in the 36th minute from a breakaway.
Jordan Obita had a free-kick blocked by the defensive wall at one end and Blackburn swiftly counter-attacked. Chris Gunter made a poor attempt at a clearing header and Jordan Rhodes won the ball off Gorkss and fed Conway.
Conway's low cross-shot appeared to be heading wide of the far post, but took a generous deflection off McAnuff on its way past home keeper Alex McCarthy. It was Conway's first start for Blackburn since signing from Brighton on transfer deadline day.
McCarthy prevented Rhodes from making it 2-0 soon after with a fine save from his fierce driv, and Rovers also went close after the break, when no one was on hand to touch home Tommy Spurr's superb skidding cross from the left.
Reading boss Nigel Adkins had seen enough and made a triple substitution in the 62nd minute, bringing on Hal Robson-Kanu, Royston Drenthe and Danny Guthrie.
It almost worked instantly with Obita's centre evading everyone apart from Drenthe at the far post, but the former Real Madrid midfielder scuffed his shot wide.
Drenthe went closer, with a powerful attempt that just cleared the crossbar, but Blackburn held on comfortably, despite more than nine minutes of stoppage time.